1. Field of the Invention
The present invention relates to an operation-staggered dual switch whose first and second switching mechanisms are so designed that their turning "on" or actuation may be staggered in time, thereby for instance, preventing the flow of rush current in an electric motor when starting.
2. Description of Related Art
In starting the electric motor a heavy rush current flows therein in the instant switch is turned on (see FIG. 12). The rush current causes sparks to appear between the confronting contacts of the switch when these contacts bound, and the switch is liable to be defective in its contacts.
To prevent the flowing of such rush current two switches are operatively connected so that their turning "on" may be staggered. When the first switch turns on, a resistor, coil or controlling unit is put in circuit with the electric motor to prevent the flowing of rush current therein, and then the second switch turns on to exclude the resistor, coil or controlling unit, allowing the electric motor to continue running.
One example of a staggered type of composite switch is disclosed in Japanese Utility Model 63-28817(B). When depression of the actuating knob starts against a counter spring, which sits on a seesaw-like movable contact of the second switch, the seesaw-like movable contact is caught and restricted in motion by a spring-biased retainer in the form of a fulcrum. When the actuating knob advances a predetermined distance beyond the early throw position in which the first switch turns on, the retainer is yieldingly depressed to release the seesaw-like movable contact, and then it rushes to the throw position under the counter action of the spring on the actuating knob.
Another example of a staggered type of composite switch is disclosed in Japanese Utility Model 63-34176(B). The second switch to be thrown later has a seesaw-like lever, and the seesaw-like lever has a contact fixed to one end and a damper fixed to the other end. The damper has the effect of retarding the operation of the second switch, which is thrown later than the first switch. The damper is of a dust-tight structure.
As for the former staggered type of composite switch: the spring-biased retainer applies unstable force to the seesaw-like movable contact for restricting it in motion, and the resilient force applied by the counter spring to overcome the restriction is dependent on the strength of force with which the actuating knob is depressed. As a consequence, the time at which the movable contact is released is indefinite, and sometimes the movable contact cannot be released when associated parts do not work well. After repeating the switching action many times, associated parts are liable to be worn or changed in friction, thus causing their stagger actuation times to vary after long-termed use.
As for the latter staggered type of composite switch: to change the damping characteristics of the damper it is necessary that annular membranes and inter-membrane spacers be changed, and then, silicone grease may leak and scatter from the damper cylinder. The seesaw-like contact lever turns at a speed dependent on the speed at which the actuating knob is moved, and therefore, the stagger actuation times vary with the speed at which the actuating knob is moved.